This is a single-armed, multicenter, non-blinded phase 2 study to assess efficacy of induction ipilimumab + nivolumab followed by chemoradiation to spare the bladder in urothelial bladder cancer.

This is a phase 2 study in which fifty adult patients with cT2-4aN0-2 urothelial bladder cancer, who are amenable for chemoradiation, will be included. Lymph nodes should be amenable for inclusion into the radiation field.

Included patients will be treated with three cycles of checkpoint inhibition: ipilimumab 3mg/kg on day 1, ipilimumab 3 mg/kg plus nivolumab 1 mg/kg on day 22, and nivolumab 3 mg/kg on day 43.

Response of this induction therapy will be evaluated by cystoscopy, mpMRI and a CT scan.

Patients will then be treated by radiation to the bladder and involved nodes, in combination with mitomycine C (day 1, 12 mg/m2, maximum dose of 20 mg) and either daily capecitabin or intravenous 5-FU in week 1 and 4. Radiotherapy will be delivered using Volumetric Modulated Arc Therapy delivering a dose of 50Gy to the whole bladder with a simultaneous tumor boost of 60Gy to the tumor bed.

The primary endpoint is efficacy, defined as bladder-intact event-free survival (BI-EFS). Events consist of death by any cause; muscle-invasive, upper urinary tract, nodal or distant recurrence, cystectomy, or switch to cisplatin-based chemotherapy.

The first evaluation after completion of chemoradiation will be after three months. Further follow-up visits will take place 6, 12, 18, 24, 30, and 36 months after completion of chemoradiation. During these visits, focused physical examination, cystoscopy and a CT chest-abdomen will be performed, combined with registration of treatment-related adverse events and a questionnaire for evaluating QoL, bladder function and long-term effects of immunotherapy on QoL.

Key secondary endpoints are overall survival (OS), recurrence-free survival (RFS), feasibility to proceed to chemoradiation, safety, QoL, and bladder function.

Inclusion Criteria:

1. Willing and able to provide informed consent
2. Age ≥ 18 years
3. Patients with cT2-4aN0-2M0 urothelial bladder cancer, who are amendable for chemoradiation and who are seeking an alternative to radical cystectomy and/or patients who are medically unfit for surgery.
4. Lymph nodes should be amenable for inclusion into the radiation field.
5. World Health Organization (WHO) performance Status 0 or 1.
6. Urothelial cancer is the dominant histology (>70%). A small cell component is not allowed.
7. Formalin-fixed paraffin-embedded (FFPE) tumor specimens in paraffin blocks from diagnostic TUR available.
8. Screening laboratory values must meet the following criteria: WBC ≥ 2.0x109/L, Neutrophils ≥1.0x109/L, Platelets ≥100 x109/L, Hemoglobin ≥5.5 mmol/L, GFR>30 ml/min as per Cockcroft-Gault formula, AST ≤ 2.5 x ULN, ALT ≤2.5 x ULN, Bilirubin ≤1.5 X ULN
9. Negative pregnancy test (βHCG in urine or blood) for female patients of childbearing potential within 2 weeks prior to day 1 of start immunotherapy.
10. Highly effective contraception for both male and female subjects if the risk of conception exists. Female patients of childbearing potential must comply with contraception methods as requested by the study protocol.

Exclusion Criteria:

1. Previous pelvic irradiation
2. Upper tract urothelial cancer
3. Extensive carcinoma in situ (CIS) of the bladder
4. Bilateral hydronephrosis
5. Previous intravenous chemotherapy for bladder cancer
6. Contra-indication to one of the study treatment components, or mpMRI
7. Subjects with active autoimmune disease in the past 2 years. Patients with diabetes mellitus, properly controlled hypothyroidism or hyperthyroidism, vitiligo, psoriasis or other mild skin disease can still be included.
8. Documented history of severe autoimmune disease (e.g. inflammatory bowel disease, myasthenia gravis).
9. Prior CTLA-4 or PD-(L)1 -targeting immunotherapy.
10. Known history of Human Immunodeficiency Virus, active tuberculosis, or other active infection requiring therapy at the time of inclusion.
11. Positive tests for Hepatitis B surface antigen or Hepatitis C ribonucleic acid (RNA)
12. Underlying medical conditions that, in the investigator's opinion, will make the administration of study drug hazardous or obscure the interpretation of adverse events
13. Medical condition requiring the use of immunosuppressive medications, with the exceptions of intranasal and inhaled corticosteroids or systemic corticosteroids at physiological doses, which are not to exceed 10 mg/day of prednisone, or an equivalent corticosteroid. Steroids as premedication for hypersensitivity reactions (e.g., CT scan premedication) will be allowed.
14. Use of other investigational drugs four weeks before study drug administration
15. Malignancy, other than urothelial cancer, in the previous 2 years, with a high chance of recurrence (estimated >10%). Patients with low risk prostate cancer (defined as Stage T1/T2a, Gleason score ≤ 6, and PSA ≤ 10 ng/mL) who are treatment-naive and undergoing active surveillance are eligible.
16. Pregnant and lactating female patients.
17. Major pelvic surgical procedure within 4 weeks prior to enrolment or anticipation of need for a major surgical procedure during the course of the study other than for diagnosis.
18. Severe infections within 2 weeks prior to enrolment in the study including but not limited to hospitalization for complications of infection, bacteremia, or severe pneumonia.